1. Field of the Invention
The invention relates to an end mill.
2. Description of Related Art
Such end mills are basically known, for example from DE 103 25 600 B4 or the “Pilot Mill” journal of the applicant from 2013.
Milling tools of this kind have more recently been used when holes, including deep holes, have to be introduced at an inclination to a work piece surface. In this case, the face mill is used to “chamfer” the work piece surface or provide it with a pilot hole, which during the ensuing hole machining process serves as a guide for the drill, for example a gun drill.
The incremental improvements made to the materials for the used tools have also been accompanied by a rising quality of such pilot holes and chamfered surfaces. Improving the stiffness of the tools, for example by using hard materials like solid carbide (VHM), makes the dimensional accuracy of the pilot holes very good even if they are introduced into the work piece at a relatively large angle to the surface normal. Further improvements to machining quality in terms of position, dimensional accuracy and machined surface can be achieved by offsetting the front cutting edges relative to each other by unequal angular pitches (see DE 103 25 600 B4). Another measure involves assigning a negative front rake angle to the circumferential cutting edges to give the tool enough stability for machining high-strength and high-viscosity materials.
It has been found that the known geometries of the generic face mills are often inadequate for maintaining the required dimensional accuracies of the pilot holes, which by now range between 3 and 6 μm for permissible roundness deviations.